test/e2e: optimize RunFrps/RunFrpc with process exit detection

Refactor Process to track subprocess lifecycle via a done channel,
replacing direct cmd.Wait() in Stop() to avoid double-Wait races.
RunFrps/RunFrpc now use select on the done channel instead of fixed
sleeps, allowing short-lived processes (verify, startup failures) to
return immediately while preserving existing timeout behavior for
long-running daemons.

test/e2e/framework/process.go

@@ -76,7 +76,10 @@ func (f *Framework) RunFrps(args ...string) (*process.Process, string, error) {
 	if err != nil {
 		return p, p.Output(), err
 	}
-	time.Sleep(2 * time.Second)
+	select {
+	case <-p.Done():
+	case <-time.After(2 * time.Second):
+	}
 	return p, p.Output(), nil
 }
 
@@ -87,7 +90,10 @@ func (f *Framework) RunFrpc(args ...string) (*process.Process, string, error) {
 	if err != nil {
 		return p, p.Output(), err
 	}
-	time.Sleep(1500 * time.Millisecond)
+	select {
+	case <-p.Done():
+	case <-time.After(1500 * time.Millisecond):
+	}
 	return p, p.Output(), nil
 }